1. Field of the Invention
The present invention relates generally to a system for data acquisition and transmission. More particularly, the present invention relates to transmitting radiological images from a base radiology site to a remote site.
Teleradiology involves the transmission of digitized radiological images to an off-site or receive location for medical diagnosis purposes. The most common transmission site is a hospital; the usual receive site is the doctor's home or office.
When a patient or trauma victim is brought into a hospital, the patient may undergo one or more radiological processes. Current radiological processes include CAT or CT Scan (Computerized Axial Tomography), Magnetic Resonance Imaging (MRI), Nuclear Medicine Imaging (NMI), Ultrasound and X-ray. Depending on schedules, work-load, emergencies, budget constraints, etc., a radiologist may not be available in the hospital at any given time to read the image(s). With teleradiology, a radiologist can expand the territory covered by reviewing transmitted images at a remote office or site. Most frequently, the images are transmitted over standard telephone lines. However, with the advent of cellular telephones, digital cellular radio, fiber optics, and satellite communications, transmission medium is no longer limited to standard telephone lines.
In practice, an imaging or radiological device scans the traumatized tissue. The raw digitized data is converted to a video signal and displayed on the associated monitor or display device. Most imaging or radiological devices utilize a means for storing the raw data. Further, most imaging devices compress the raw data before it is stored. The most common storage devices are disc drives (either 8 inch, 5.25 inch or 3.5 inch), tape drives or laser disc drives. The storage medium is for archival purposes.
A radiological cross-sectional scan of a particular area of a patient's body is called a "slice". The slices are typically five (5) millimeters apart. A collection of slices is called a study. Although it may contain any number of slices, a typical study usually contains from 20 to 40 slices.
A data matrix may be used to depict each slice. The most common data matrix consists of 256 by 256 available data points. However, the matrix size can vary. For example, the Elscint CT Scan, model no. 1800, allows the operator to choose from three different matrix sizes, namely 256.times.256; 340.times.340; and 512.times.512. Each point within the matrix may be given a density value. A density value represents the density of the material found at a specific point within a slice.
Most CT scanners employ the Houndsfield scale to assign a numeric value to each density value. The Houndsfield scale ranges from minus 1000 to 3095. Air is assigned the numerical value of minus 1000, water is assigned the value of zero, and bone is assigned density values from 200 and up.
When viewing a slice, the radiologist is not looking at the entire range of the Houndsfield scale. Before a slice is displayed, the radiologist designates a "window". The window is a narrowing filter. In some instances, the window blocks as much as 98% of the raw data. A tissue window would be defined to check for internal bleeding and a bone window would be defined to check for bone fractures.
For example, if soft tissue is of particular interest, the radiologist defines a window ranging from zero to 100. In this example, any density value below zero appears as black on the CRT screen and any density value above 100 appears white. Density values within the defined range appear as shades of gray.
Nuclear Medicine Imaging devices use an analogous system to count the radioactive particles. The method of injecting a radioactive dye into a patient and measuring the radioactive particles given off, as the radioactive material decays, is known to those skilled in the art. An NMI device "counts" or detects the number of radioactive particles emitted. The count starts at zero and continues upwards.
Displaying all of the information at once, i.e., viewing soft tissue windows simultaneously with bone windows, would be virtually useless since there would be too many shades of gray for the human eye to distinguish between.
2. Description of the Prior Art
The typical teleradiology system utilizes available hardware and software to transfer video data from an imaging or radiological device to a remote viewing device. All known prior art teleradiology systems capture the filtered analog video signal generated by the radiology equipment and convert it to digital data by using a video digitizer or frame grabber. The frame grabber is usually connected to the video output jack of the radiological device's monitor. The frame grabber digitizes the analog video signal and forwards the digitized data to the teleradiology transmit computer. The digitized data is then transmitted to the remote location using a modem and standard telephone equipment. At the receiving site, the digitized video data is received by a second modem and converted back to a video signal and displayed on the remote CRT for the radiologist.
When the radiology equipment produces a plain film, e.g., an X-ray negative, a slightly different procedure is required. The film is placed on a light box. A video camera is pointed at the light box and the video signal from the video camera is connected to the frame grabber. The digitized data is then sent to the base site teleradiology computer for transmission to the remote site. Again, prior art teleradiology systems transmit the digitized video signal to the remote location.
In the normal operation of a prior art teleradiology system, an operator or technician located at the base or transmit site, establishes a communication link with the remote site. The radiologist conveys to the technician the desired windows and slices for viewing. The technician reviews the patient study by viewing the radiology device's monitor. The technician, in accordance with the doctor's instructions, selects a window and a slice. The raw digital data associated with the slice is filtered through the selected window. As a result of this filtration, raw data is lost. The filtered data is then converted to an analog video signal and displayed on the radiological device's monitor or CRT screen. The operator views that slice on the screen and decides whether to transmit that particular image to the remote site. If the technician decides that the slice is to be transmitted, the frame grabber of the teleradiology system is instructed to digitize the displayed image. The frame grabber responds by taking a digitized "snap-shot" of the image shown on the radiological device's display screen. The digitized data is then stored within the teleradiology system's transmit computer. The operator then repeats this process for each desired slice until the study is complete. This is a time consuming process. Furthermore, raw data has been lost since it has been filtered, converted into an analog video signal and then reconverted into a digital signal.
After completing the collection of filtered data, the technician advises the doctor that the desired study is ready for transmission to the remote site. The doctor at the remote site prepares to receive the information. The computer modems connect to establish a link and the data is transferred. The doctor will review the filtered data on the remote screen and may be able to make a preliminary diagnosis at this point. If the radiologist requires additional information, usually the same study using a different window, the doctor contacts the technician with instructions to set the new window and transmit the study.
The prior art teleradiology devices do not allow the radiologist at the remote site to control the true filtering or the true windowing of the images. Only a portion of the information available at the time the initial window is selected at the hospital can be sent to the remote site. If the radiologist wants to view the study with a different window filtering, the radiologist must instruct a technician at the hospital to refilter the study. After the frame grabber digitizes the signal and stores it within the base computer, it is transmitted to the remote site.
The technician must instruct the sending unit to digitize each slice as it is displayed on the base radiological device's CRT. The process needlessly occupies the technician's valuable time. Further, it increases the time before the radiologist has access to the information needed to make a diagnosis. This delays the treatment of the patient.
After receiving the requested data, the radiologist views the images, makes a preliminary diagnosis and instructs the hospital about the prescribed treatment. Usually, the radiologist at the remote site cannot make a final diagnosis on existing teleradiology systems since the raw data is not transmitted. At a later time, usually the next day, the radiologist will go to the base site and will review the study again with all available data to make a final diagnosis.
Since prior teleradiology systems only use the video signal, valuable information is not transmitted to, or viewed by the radiologist at the remote site. In prior art teleradiology systems, the doctor at the remote location can usually do no more than to look for gross abnormalities, such as fractures.